Is it a problem to offer my own or “third-party” products in my shop in addition to Shirtee.Cloud products?
No, it no problem.
Only orders of items from Shirtee.Cloud are received and get processed by us. If someone orders a Shirtee.Cloud article and one that you for example store and ship yourself, your customer will receive several packages.
If you want to store everything in one place and have it shipped in the same package, check out our warehousing options.